The present invention pertains generally to an improvement in dispensers for metering out particulate materials such as shot, metal or plastic parts, medicinal capsules and other items which it is desired to measure and divide into accurately predetermined quantities without damaging or jamming the materials in the metering device. The invention finds special application to machines for loading shotshells, but is not limited to that use alone.
A typical shotshell loading machine of a kind in current use is described by U.S. Pat. No. 2,663,421 to Reynolds et al, which has now expired. A shot dispenser or charger according to that patent feeds shot by gravity from a hopper into a metering trap chamber formed in a slidable charging plate, which is then moved to align the trap chamber with a funnel through which the shot drops into a waiting shell.
The charging plate is reciprocated to transfer the trap chamber back and forth between the hopper and the funnel, and thus meters out successive hopefully-equal charges of shot, whose volume is intended to be predetermined by the size of the trap chamber. The hopper outlet is sealed off by the upper surface of the charging plate to stop the flow of shot each time the trap chamber slides away from the outlet. Often, however, one or more extra shot become trapped between the outlet and the sliding surface of the plate, and interfere with the sliding motion; this because the clearance between the hopper and the plate must necessarily be less than the diameter of the shot, to keep the shot from escaping. In the case of a material having a relatively low shear strength, such as lead shot, this interference does not jam the dispenser; the charging plate merely severs the interfering shot, whose cutoff bottom fragments fall into the trap chamber and are then discharged into the shell. This represents some waste of shot, since the irregular fragments will of course not follow a normal, predictable trajectory when the shell is fired. The destruction of a portion of some products dispensable into measured packages by such a mechanism, e.g. screws or medicinal capsules, would represent a more severe loss. In connection with loading lead shot, however, this drawback has been accepted for many years, as no satisfactory solution has been presented in this type of metering device.
At the present time, there is considerable concern about the recently-discovered penchant of ducks and other aquatic fowl to swallow lead shot accumulated in marshy hunting areas. The ingested shot become disintegrated in the fowl's craw, and are thought to result eventually in lead poisoning. Attention has therefore turned to proposals for substitution of steel shot, or combination iron and lead shot, to avoid this possibility. Various coatings for lead shot have also been proposed, but a duck's craw is a very effective grinding mechanism, being filled with sand and grit for this very purpose, so that any known coatings are soon worn away. There is no clear indication as yet that steel or iron shot will be adopted as a standard load for waterfowl, for the reason that the lesser density of these materials reduces the impact energy of the individual shot pellets; in consequence, it may develop that their use gives rise to an increased incidence of crippling wounds, which could result in delayed deaths as wasteful and cruel as any caused by lead poisoning. Be that as it may, extensive use of steel shot is anticipated, in the hope of overcoming the problem.
Steel and iron shot cannot be satisfactorily metered out by the conventional shot dispensers previously described, as the shear strength is too great; either the charging plate jams on interfering shot, or something must yield, and the plate becomes damaged very quickly.